The present invention contemplates synthesis gas creation via gasification of carbonaceous materials producing a synthesis gas containing CO, CO2, and H2 that can be further acted upon by fermentation or digestion by certain microorganisms to produce alcohols (methanol, ethanol, propanol, butanol, etc.), acetic acid, acetates, hydrogen, etc. The following reactions and discussion are illustrative of an embodiment of the present invention involving alcohol production; which is used as the example product in the following description of the concept:6CO+3H2O→CH3CH2OH+4CO2  (1)6H2+2CO2→CH3CH2OH+3H2O  (2)CO2+C2CO  (3)CO2+H2CO+H2O  (4)CH4+CO22CO+2H2  (5)
The quantity of alcohols produced depends upon the efficiency of the gasification and fermentation processes. There exist many inefficiencies in gasification including various energy requirements involved in preparing carbonaceous feedstock, feeding carbonaceous feedstock, raising carbonaceous feedstock temperature, maintaining carbonaceous feedstock temperature, utilizing various oxygenates in each of the previous aspects of the present invention, inadequate oxygenate contact with carbonaceous feedstock, energy losses to the environment, endothermic reactions, air leakage in pressure units, and incomplete conversion of carbonaceous feedstock to CO and H2. Use of low bulk density carbonaceous feedstock provide inefficiencies including: hot spots, over exposure to oxygenates, decreased CO concentrations, slagging of ash, etc. The type and quantity of oxygenate added can enable temperature control and increase alcohol production. These and other inefficiencies decrease the CO and H2 available in the resultant synthesis gas which can negatively impact alcohol production.
The fermentation step can also negatively impact alcohol production via: incomplete conversion of CO or H2, incomplete utilization of CO or H2, undesirable byproduct production, undesirable byproduct induced inhibition, undesirable product induced inhibition, loss of cell mass, etc. Microorganisms, in some cases, participate in greater CO conversion than H2 conversion. Hence, higher CO concentrations can provide for greater alcohol production. For ethanol production from biomass using acetogenic bacteria, the ethanol production can be about 80 gallons per dry ton (gal/DT) of carbonaceous feedstock. Not utilized or unconverted carbon can remain as carbon dioxide.
It is believed that carbonaceous feedstock conversion to alcohols can assist in decreasing the carbon footprint on the environment. Alcohol production via the present invention can increase carbon utilization for fuel production; thus having a tremendous potential to positively impact climate change by improving the carbon efficiency. Further, the present invention provides a means to decrease dependence on foreign oil and increase global energy stability.
Carbon dioxide reforming is known in the art, however, converting carbonaceous material into fuel is still of technological significance and interest. The present invention applies to the gasification and/or fermentation process with the purpose of increasing the yield of alcohol (fermentation products) by Equations (1) to (5), as well as improving the efficiency of gasification of certain carbonaceous feedstock. The present invention also provides a means of reducing greenhouse gas emissions by sequestering the carbon into liquid transportation fuel alcohols; thus decreasing dependence on petrochemical fuel sources.
Gasification of corn stover and other biomass materials often result in excessive temperatures and melting of the ash (slagging), with no ready method for removal of this slag. This problem is particularly prevalent when using pure or enriched oxygen as the oxidant. In addition, when using biomass raw materials, the carbon monoxide composition of the synthesis gas is often quite dilute (especially with air as the oxidant), resulting in a low heating value and a less desirable gas for subsequent conversion to electricity, chemicals or fuels. Carbon dioxide is a global warming gas and is readily available from combustion processes or from certain chemical or biological reactions, such as production of ethanol via sugar fermentation from grain or cane. Carbon dioxide concentrations are increasing in the Earth's atmosphere as a result of fossil fuel consumption. A means of converting CO2 into liquid fuel could significantly assist reducing CO2 concentrations in the Earth's atmosphere and could aid in reducing CO2 emissions.
Grain and sugar cane ethanol processes require significant amounts of steam and electricity for feedstock preparation, ethanol purification, etc. As energy costs have increased, these items represent a major cost component in production of ethanol. Furthermore, during the harvesting of the grain or sugar cane, half or more of the crop is in the form of biomass, such as corn stover or sugar cane leaves and bagasse, which is largely unused. This biomass could be used to produce energy and or additional ethanol with the appropriate conversion process.
Various strains of acetogens (Drake, 1994) have been described for use in the production of liquid fuels from syngas: Butyribacterium methylotrophicum (Grethlein et al., 1990; Jain et al., 1994b); Clostridium autoethanogenum (Abrini et al., 1994); Clostridium ljungdahlii (Arora et al, 1995; Bank et al., 1988; Barik et al. 1990; and Tanner et al., 1993). Of these, Clostridium ljungdahlii and Clostridium autoethanogenum are known to convert CO to ethanol.
U.S. Pat. No. 5,173,429 to Gaddy et al. discloses Clostridium ljungdahlii ATCC No. 49587, an anaerobic microorganism that produces ethanol and acetate from CO and H.sub.2O and/or CO.sub.2 and H.sub.2 in synthesis gas.
U.S. Pat. No. 5,192,673 to Jain et al. discloses a mutant strain of Clostridium acetobytylicum and a process for making butanol with the strain.
U.S. Pat. No. 5,593,886 to Gaddy et al. discloses Clostridium ljungdahlii ATCC No. 55380. This microorganism can anaerobically produce acetate and ethanol using waste gas (e.g. carbon black waste gas) as a substrate.
U.S. Pat. No. 5,807,722 to Gaddy et al. discloses a method and apparatus for converting waste gases into useful products such as organic acids and alcohols using anaerobic bacteria, such as Clostridium ljungdahlii ATCC No. 55380.
U.S. Pat. No. 6,136,577 to Gaddy et al. discloses a method and apparatus for converting waste gases into useful products such as organic acids and alcohols (particularly ethanol) using anaerobic bacteria, such as Clostridium ljungdahlii ATCC Nos. 55988 and 55989.
U.S. Pat. No. 6,136,577 to Gaddy et al. discloses a method and apparatus for converting waste gases into useful products such as organic acids and alcohols (particularly acetic acid) using anaerobic strains of Clostridium ljungdahlii. 
U.S. Pat. No. 6,753,170 to Gaddy et al. discloses an anaerobic microbial fermentation process for the production of acetic acid.
U.S. Pat. No. 7,285,402 to Gaddy et al. discloses an anaerobic microbial fermentation process for the production of alcohol.
Other strains of microorganisms have also been described for use in the production of liquid fuels from synthesis gas, e.g.: Butyribacterium methylotrophicum (Grethlein et al., 1990, Appl. Biochem. Biotech. 24/24:875-884); and Clostridium autoethanogenum (Abrini et al., 1994, Arch. Microbiol. 161:345-351).
Numerous conventional methods exist for gasification, synthesis gas creation, and synthesis gas fermentation. However, these methods suffer from numerous inefficiencies. There remains a need for additional more effective methods for gasification, additional more effective methods for gasification for use with synthesis gas, additional more effective methods for gasification for use with synthesis gas fermentation process, additional methods to effectively reduce CO2 concentrations in the atmosphere, additional methods to effectively decrease CO2 emissions, and additional methods to effectively sequester CO2.